The combining of two or more liquids together to a desired concentration and/or other characteristics or properties, such as pH, conductivity, optical density, refractive index, etc., of the constituent liquids is fundamental to many industrial processes and commercial products. This combining of liquids may be referred to as blending and is common in many industrial segments. In addition, blending systems find use in the field of liquid chromatography where blended liquids are provided to chromatography columns to permit the separation of mixtures for analysis or for purification purposes.
On site blending systems provide many advantages over purchasing pre-mixed chemicals. By using a blending system, a single quantity of feedstock concentrate can be used to produce many times its volume in diluted solution, depending on the desired concentration of the dilution. Thus, a single feedstock concentrate, used to produce the equivalent of many feedstocks of dilute liquid via, a blending system can greatly reduce facility costs associated with fabrication of large tanks, floor space required, validation and quality control costs to confirm makeup, as well as spoilage and disposal costs of non-compliant out of date or unused blended solutions. Freight costs associated with chemical delivery can also be reduced. In addition, onsite dilution and blending increases the variety of chemical concentrations and mixtures that are immediately available, without requiring a corresponding increase in the number, of feedstocks and chemicals that must be purchased, thereby reducing facility and operating costs and providing the logistical and administrative advantage of reduced inventory.
High accuracy in terms of concentration for blending systems providing liquids to liquid chromatography systems is desirable. In addition, quality control concerns favor increased blending accuracy for liquids that are provided to industrial processes and that are used to create commercial products. Indeed, Six Sigma quality control principles dictate that lower variability in an industrial process results in a greater percentage of higher quality products being produced by the industrial process.
It is well known, however, that there will be variations in concentration within a feedstock. For example, it is common for different portions of a large feedstock tank filled with a solution to have different proportionate mixtures of the constituent liquids. Gradients exist in large feedstocks in terms of both concentration and temperature. As a result, liquid provided from the feedstock will vary in terms of concentration, which poses challenges for accurate analysis, quality control analysis, and uniform delivery to a process. Feedstock solvents, commercially supplied, have variations in actual concentration from batch to batch, as well as innate impurities, which prevents 100% pure concentrations from being available in bulk supply. In response, systems and methods for accurately blending liquids from such feedstocks, such as the Inline Buffer Dilution systems and methods using Process Analytical Technology (PAT) in commonly assigned U.S. Pat. Nos. 7,072,742; 7,515,994 and 8,271,139, all to Bellafiore et al., have been developed.
When a blend is simply a dilution of a buffer concentrate with water or other diluent, it is known as a binary blend. When a blend is accomplished by way of dilution of multiple buffer concentrates with water or other diluent, it is known as a ternary blend when it has three components, a quaternary blend when it has four components, and so on with names indicating the number of components being blended. A common example of ternary blending is when two concentrate solutions are simultaneously diluted with water or other diluent to form a specific ternary blend. The inlet concentrates may be of any form, such as salts or conjugate forms of a buffer, or a form of a buffer (concentrate) that is to be tempered with a form of an acid or base.
A less common example of ternary blending is the incorporation of refractive index (RI) inline process measurement with conductivity inline process measurement. Temperature control can be incorporated in such examples (and in other cases) in order to reduce the matrix effect of temperature to two measures, two variables.
Factors such as target conductivity, pH, and/or other component concentration of the blend can be significant with respect to the process application to which the blend is applied. The processes these blends are used for are greatly diversified but in general, may be used to feed a final product manufacturing process, biological growth, separation or purification process, etc.
As described in the commonly assigned U.S. Pat. Nos. 7,072,742; 7,515,994 and 8,271,139, the special purpose of the Inline Buffer Dilution equipment using PAT is the ability to consistently obtain the target conductivity and/or pH and/or other component concentration of the blend independent of upstream variability which may occur in the inlet concentration of the buffer concentrates or diluent composition. Due to the limitations of the analytical technologies available for PAT feedback/control, however, it is sometimes necessary to construct blends using flow control and flow meters as the feedback (to the programmable logic controller) to proportion two or more components in the blend. A drawback of the Inline Buffer Dilution equipment using flow control is the flow meter's inability to compensate for the potential/inherent variability of the inlet buffer (or diluent) concentration. Specifically, flow control fundamentally cannot be used to target desired pH within commonly acceptable precision. Thus, in a ternary blend where flow control is used to accomplish the target blend between the first concentrate buffer and the diluent, and pH control is desired, pH feedback/control of the second concentrate buffer must be used to accomplish pH tempering to a high degree of precision.
In some circumstances in the above scenario, the second inlet buffer concentrate being used for pH tempering (or tempering of conductivity or other property) must be a binary mixture containing as its minority component the compound which is the majority component of the first buffer concentrate. As a result, when the diluent and the first buffer concentrate must be proportioned by flow control, the proportion between the diluent and the first concentrate being controlled by flow would, by the addition of the (for example) pH tempering solution, with its minority component being the same as the first buffer concentrate, be unaccounted for in volume added to the final solution and spoil the proportion intended between the first buffer concentrate and the diluent. A need therefore exists for a system and method that addresses these issues.